Blowby versus engine load

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I've driven past this very spot over 4,500 times (more than double that if you count going the other way at the other part of the day)...and I have noticed this effect, but only yesterday it sunk in.

As I come into town, I can see the train lines as they come into/out of town. One line is oiled heavily, the other is pristine...
IMG_07571.jpg


Train lines being what they are, the traffic in both directions must be the same, bar a possible few handfuls of retired trains.

Trains on the left are climbing s slight grade into town (grade saves brakes as they slow into town)...they are also loaded (typically with coal) as they head that way towards the coast (power stations and export)...all engines running.

Thus the ones on the left are running hard, at load, and blowing by their crank breathers...on the right, they are on the return trip, unloaded, and still powering slightly, with not all engines running.
IMG_07581.jpg


This is pretty typical, three engines (first two were running), and empty coal cars (100 tonne each, 80 tonne coal to fill them)...

Amazing what a difference 3,500 tonnes on the drawbar will do.
 
Excellent picture (beautiful view too!) that shows the results of engine loading.

I used to work on off-road dumps that had to struggle out of a strip....the road showed the loads the 12V71's were subjected to. Down travel only showed tire tracks and the typical DD droppings.
 
Originally Posted By: Miller88
I'm not sure that's so much blowby as it is "rolling coal"


He's talking about the breather tubes dumping out oil on the track. Notice how one track is clean and the other is dirty.
 
There is always more blowby on a lightly loaded engine. The heavier the load, the greater the seal is on the piston rings.
 
Originally Posted By: motor_oil_madman
Originally Posted By: Miller88
I'm not sure that's so much blowby as it is "rolling coal"


He's talking about the breather tubes dumping out oil on the track. Notice how one track is clean and the other is dirty.


Ha! Didn't even notice that.

Makes sense. Especially on a turbodiesel. Pulling a hill that has to be pretty heavily loaded and at full boost.
 
Another possibility is a privatly owned train that runs the same tracks every time and has a leak. As kids we would stand under a bridge as the train went over us only to come out covered in dirty oil.
 
Originally Posted By: Chris142
Another possibility is a privatly owned train that runs the same tracks every time and has a leak. As kids we would stand under a bridge as the train went over us only to come out covered in dirty oil.



That wasn't oil bud.
The toilets empty on the side of the tracks. That's why they don't let you use the toilets when stopped at a station.


Hehehe
 
Originally Posted By: Vikas
Bus is the load same in both the direction?


3500 tonnes more coal on board heading left to right across the page. Slight grade coming up into town.
 
Originally Posted By: motor_oil_madman
There is always more blowby on a lightly loaded engine. The heavier the load, the greater the seal is on the piston rings.


While that makes sense, it doesn't seem to match my observations. For example tractor pulling engines appear to put out more blowby when loaded heavily. But to be fair, I didn't see them operate at the same RPM's unloaded.
 
It's not really "oil being dumped on the tracks", it's crankcase breather fumes, that contain some soot, air, exhaust gasses, and yes, oil.

They are puffed out the breather under load, and as trains run in pretty well defined paths, they locate where they do...It's a fine spray, and probably about as biodegradable form as it can be versus pools/streams of the stuff. Massive surface area, exposed to oxygen and UV etc.

Mental exercise for you...say each tyre loses 1lb of rubber dust during it's life, and 200M tyres are sold in the US each year, how much rubber dust is "dumped" right on the road
 
Yep. I have always called the blowby vaporing. An older unloaded 2-stroke Detroit will typically drip oil after idling for a while whereas one under heavy load will "vapor" and the vapor is exactly as Shannow described.

A lot of 4-strokes with open crankcase ventilation vapor too and the end of the hose will usually be a little oily feeling. Our ISM's put out quite a bit....enough that it's very noticable under a bus.
 
I remember when I was a kid back in the 60's when most cars and trucks still had draft tubes vs PCV. The roads had heavy black streaks down the center from this. The streaks were heavier going up a grade compared to the downhill side.
I notice that today we don't have this as much, but if you are attentive, you can spot a dip or bump in the road by the oil streaks from drips that are knocked off the vehicle by the bump.
 
Yep....I watch for the blackened "dips" and time my coffee sips around them. You are absolutely correct, there are way less of the highway streaks now with PCV systems and tighter engines.
 
Toll colours, we still have some locos painted like that. The thread would turn political if I explained why, although why our politics would be a concern here I have no idea.
 
Originally Posted By: JetStar
Originally Posted By: motor_oil_madman
There is always more blowby on a lightly loaded engine. The heavier the load, the greater the seal is on the piston rings.


While that makes sense, it doesn't seem to match my observations. For example tractor pulling engines appear to put out more blowby when loaded heavily. But to be fair, I didn't see them operate at the same RPM's unloaded.


I agree. I would think there would be more blowby when loaded. Yes, the ring seal may be a little better under load but not that much better.

I believe there is some other explanation for the dirty track.
 
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